allow locs to be passed to some Ast_builder functions
allow locs to be passed to some Ast_builder functions

Summary: allows these functions to be used outside of tests, where we actually care about locs, and to write tests that care about locs.

Reviewed By: motiz88

Differential Revision: D13625377

fbshipit-source-id: 8e85915795034733e5288ea34718692fad8ea6d4

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